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Old 11-08-2017, 08:10 AM   #1
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Prop size for 1999 Mainship Pilot 30

We have just purchased this boat and are dealing with vibration at top speeds. We just got hit with Hurricane Irma so I am less than excited to get into the canal and none of the marinas are pulling boats out in my area (all are closed).

I have a Yanmar 240 (previous owner had the engine recently replaced as a marina put GAS into it!) and I BELIEVE the prop is 21x26, but I am not sure yet.

Does anyone know the factory prop? Does going to a 5 blade help the vibration, and if so what size/pitch?
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Old 11-08-2017, 09:05 AM   #2
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Since the boat is new to you and you probably don't have any history with this vibration, I would first align the engine to the prop shaft. When you do this check to make sure that the coupler faces are square and true to the shaft.

Then if that didn't improve the vibration, I would check to see what my true (phototached) rpm is at wot under way. If it is less than 3,400 then I would pull the prop (with a diver or haul out) and take it to a good prop shop and have the pitch adjusted so it makes 3,400 and the prop trued. Then with a dial indicator check the prop shaft for trueness while the prop is out for rework. Also check the cutless bearing for slop.

When you reinstall the prop, make sure that the prop isn't "riding on the key" by comparing the position of the prop on the shaft without the key and with.

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Old 11-30-2017, 08:10 AM   #3
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Excellent advice. Thank you. Has anyone heard of Mainship addressing this problem with a 5 blade prop?
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Old 11-30-2017, 09:06 AM   #4
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I’m sure the number of blades on the prop is not the problem.
Just my opinion though.

Check w a prop man that has established a good reputation.

Another option is to call Michigan Wheel and have all your information ready. Like beam, weight, power ect. I’m sure they will recomend a 3 or 4 blade prop. They also may comment on different blade designs. Some blade shapes have greater area w the same oa dia. And if nothing else you will learn something in your conversation.

As to WOT rpm I find what works best is the rpm that the engine makes it’s power. Or slightly better about 100rpm over rated rpm. Ideal IMO is 50rpm over. The rated rpm is NOT a redline or never to exceed rpm. It’s just where the engine makes it’s max power.
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Old 11-30-2017, 01:46 PM   #5
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Vibration at higher rpm could be from many sources; marine growth, a ding on a blade, a blade not aligned with the rest of the blades, the cutlass bearings, engine shaft alignment, prop out of balance, prop loose on the shaft, a misaligned strut, all causes of vibration.
A five blade prop may be smoother than a four blade, but will cost a lot of money to replace the four blade and it may not solve the vibration. Investigate the easiest and less expensive possible causes first.
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Old 11-30-2017, 02:37 PM   #6
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All good points, but this model is well known for a mysterious vibration at high RPM's that was addressed under warranty with a 5 blade prop. Looking into other possibilities as well, however no luck there so far.
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Old 11-30-2017, 03:05 PM   #7
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Ricor,
Oh I see your interest in the 5 blade.
Try to find an owners forum after contacting the manufacturer.
There probably is a design problem and they probably have a fix if it’s been going on awhile.
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Old 11-30-2017, 05:50 PM   #8
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Again, great idea, but... Unfortunately, Mainship sold to a new company that will not support old boats. No help in the owners forum... That is why I am trying this...
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Old 12-24-2017, 02:15 PM   #9
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My 1999 Pilot 30 had a 4 blade 21 x 21 prop and turned 2600 RPM and vibrated a lot. Tried alignment and had prop balanced and repitched to 21 x 24. Still vibrates but tops out at 2450 and plus 2.5 knots top end. If someone has put a 5 blade on an older Pilot it
would be great to hear about vibration. I know newer models due have 5 blade props standard but also have a different prop tunnel shape.
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Old 12-24-2017, 02:16 PM   #10
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Correct RPMs were 3600 before and 3450 after repitch.
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Old 12-24-2017, 09:16 PM   #11
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A loose or maladjusted engine mount can cause a vibration. They need to be set so each one takes approx. equal load.
Prop riding the key? Has that been checked for?
Any dings on the shaft or in the prop bore?
Shaft bent?
Coupling centreline checked for alignment with shaft centreline?
Coupling face trued to shaft?
Coupling free of dirt and dings/scratches at mating faces?
Cutless bearing ok?
Prop actually checked for damage and corrected?
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Old 12-24-2017, 11:44 PM   #12
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Originally Posted by C lectric View Post
A loose or maladjusted engine mount can cause a vibration. They need to be set so each one takes approx. equal load.
Prop riding the key? Has that been checked for?
Any dings on the shaft or in the prop bore?
Shaft bent?
Coupling centreline checked for alignment with shaft centreline?
Coupling face trued to shaft?
Coupling free of dirt and dings/scratches at mating faces?
Cutless bearing ok?
Prop actually checked for damage and corrected?
C, read up in the contest of it all. This is a known problem. I think it stems from the prop clearance on the hull. IOW, the tips of the props are too close to the hull. THe reason why the 5 blad solves the issuse is that they can go to a smaller diameter with 5 blades and have better prop clearance.
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Old 12-24-2017, 11:54 PM   #13
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All good advice, however these boats were known for vibration and it was corrected under warranty with a 5 blade prop. With the company out of business, it is very hard to find our what the prop was...
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Old 12-25-2017, 06:45 AM   #14
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This has been discussed may times at the Mainship Yahoo site. Clunky as hell site, but search feature works well. Has almost 20 years of experience in archives.
I just did a quick search there and had hundreds of hits, some containing prop sizes

I searched "tunnel" and then in advanced search "30" as subject and "tunnel" in message

https://groups.yahoo.com/neo/groups/mainship/info

I lived in Key West for 10 years, I'm told I had a very good time

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Old 12-25-2017, 11:51 AM   #15
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3 blade props are smooth if all else is in order.

Feel around while cruising and find out what’s vibrating. Bulkhead, deck, hull bottom ect. Then when you find the vibrator support it or otherwise stiffen it up so the vib or buzz is gone or greatly reduced. And finding what’s vibrating usually will lead to the source. And when you’re done there may well be less vibration than originally.

One should check that the mounts are for the correct weight range. And most often fwd mounts are lighter rated (softer) than aft because aft there is the addition of flywheel and gearbox weight. Best (I think) is to have equal rated mounts carrying equal loads by carefully attaching the aft mounts to the gear.
Sometimes however a rocking horse fore and aft as in pitching motion can become or be caused by harmonics. Often mounts of unequal load rating will probably break up and stop the rocking horse motion.

Was prop to hull clearance mentioned?
Oh yes I see Baker addressed that well in #12. For clearence related vib problems a three blade w quite to very wide blade tips can be better that a 4 or 5 blade prop. Wide blade tips are of course slightly less efficient. The tip vortice slaming against the hull bottom has a much greatter effect if the hull is lightly constructed right above the prop. Also a big soft blow to the hull bottom is less of a hammer than two or more small sharp raps from smal pointy blade tips. Three soft whomps is/may be better that 4 or five sharp raps. And at the same rpm the frequency of hydraulic pounding on the bottom changes w # of blades. If the problem is harmonic then the vibration could go away just from a frequency change due to of the number of blades.

I wonder if the gear ratio has been considered. Perhaps not as the prop clearence as a change in either direction would/may be unacceptable re blade loading ect.
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Old 02-10-2018, 06:52 AM   #16
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I feel your pain, i also own the same boat with 220 hp cummings same vibration called marlow they wont disclose any info i do believe a 5 blade prop is the answer i am i the process of trying to find out what size when i find out i will post
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Old 02-10-2018, 12:42 PM   #17
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I feel your pain, i also own the same boat with 220 hp cummings same vibration called marlow they wont disclose any info i do believe a 5 blade prop is the answer i am i the process of trying to find out what size when i find out i will post
Did they say why the wouldn't disclose any information??? That is BS!!! Not what I call Customer service!!! Back when it was the original Mainship those guys really helped me out with a lot of stuff!
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Old 02-17-2018, 07:46 AM   #18
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I hear you, i think they think i want something for nothing,thats not the case,thats why i'm trying to find out the solution before it gets launched this spring
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Old 05-02-2018, 07:30 PM   #19
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Still a problem...

Any luck Glennl?
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Old 05-03-2018, 06:27 AM   #20
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nothing yet, still hoping someone see's my post that has the replacement prop
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